Long Life Anode Material for Potassium Ion Batteries with High-Rate Potassium Storage

Abstract

We, for the first time, report potassium storage in carbon-modified Li₄Ti₅O₁₂ spinel (C-LTO), where the carbon coating increases the electrical conductivity from ~10⁻⁷ to ~10⁻¹ S cm⁻¹. C-LTO provides a high initial charge capacity of approximately 221 mAh g ⁻¹ at 0.2C (34 mA g ⁻¹) with about 77% retention for 200 cycles. Pre-potassiation of C-LTO electrode successfully improved initial Coulombic efficiency. The excellent electrode performance is further emphasized at high rate (3.2C, 544 mA g ⁻¹), with an initial capacity of 130 mAh g ⁻¹ and 70% retention for 1000 cycles. During the reaction in K cells, the incorporation of K⁺ ions into the cubic spinel Li₄Ti₅O₁₂ induces a biphasic reaction, namely cubic rock salt K-rich K₆LiTi₅O₁₂ and Li-rich Li₇Ti₅O₁₂ phases accompanied by Ti^4+/3+ redox, as confirmed by in-situ X-ray diffraction and ex-situ X-ray absorption analyses. The original Li₄Ti₅O₁₂ spinel is recovered upon depotassiation. In addition, full cells paired with a P3-K_0.5[Mn_0.8Fe_0.1Ni_0.1]O₂ cathode demonstrate the feasibility of applying the C-LTO electrode as an anode for high-rate and long-term potassium storage.